Process and apparatus for the continuous manufacture of phenolic resin foam in endless sheets

ABSTRACT

A process for the continuous manufacture of phenolic resin foam in an endless sheet which includes mixing expandable liquid phenolic resin with a blowing agent and an acid-containing curing agent, optionally with the addition of additives, and processing of the mixture in a temperature-controllable double belt press. The process also comprises cooling the phenolic resin to a temperature of from about 8* to 15*C., admixing a blowing agent under a high pressure with said resin to form a resin premix, mixing said resin premix with a curing agent resin to form a resin premix, mixing said resin premix with a curing agent and other foam additives to form a curable reaction mixture, continuously applying said mixture uniformily onto a moving substrate, covering the mixture on said substrate with a continuous protective layer, passing the covered mixture into the double belt press, and foaming the mixture under pressure until a desired sheet thickness has been obtained.

United States Patent 1191 Bruning et a1.

1 1 May 20, 1975 PROCESS AND APPARATUS FOR THE CONTINUOUS MANUFACTURE OFPHENOLIC RESIN FOAM IN ENDLESS SHEETS [75] Inventors: Klaus Bruning;Hans Junger;

Wolfgang Pungs; Peter Rheinfeld, all of Troisdorf; Franz Weissenfels;Michael Wienand, both of Siegburg, all of Germany [73] Assignee: DynamitNobel AG, Troisdorf,

Germany [22] Filed: Dec. 4, 1972 [21] Appl. No.: 311,913

[30] Foreign Application Priority Data Dec. 2, 1971 Germany 2159726 [52]US. Cl. 264/46.2; 260/2.5 F; 264/46.4;

264/53; 264/DIG. 2; 425/4 [51] Int. Cl..... B32b 5/18; B32b 11/06; C08g53/10 3,726,952 4/1973 BOCIen et a] 264/53 3,730,660 5/1973 Raffenberg264/47 FOREIGN PATENTS OR APPLICATIONS 438,703 12/1967 Switzerland264/D1G. 2 1,090,741 11/1967 United Kingdom 260/2.5 F 1,959,904 7/1970Germany 264/D1G. 2

Primary ExaminerRonald W. Griffin Attorney, Agent, or Firm-Craig &Antonelli [57] ABSTRACT A process for the continuous manufacture ofphenolic resin foam in an endless sheet which includes mixing expandableliquid phenolic resin with a blowing agent and an acid-containing curingagent, optionally with the addition of additives, and processing of themixture in a temperature-controllable double belt press. The processalso comprises cooling the phenolic resin to a temperature of from about8 to 15C., admixing a blowing agent under a high pressure with saidresin to form a resin premix, mixing said resin premix with a curingagent resin to form a resin premix, mixing said resin premix with acuring agent and other foam additives to form a curable reactionmixture, continuously applying said mixture uniformily onto a movingsubstrate, covering the mixture on said substrate with a continuousprotective layer, passing the covered mixture into the double beltpress, and foaming the mixture under pressure until a desired sheetthickness has been obtained.

30 Claims, 3 Drawing Figures PATENTEU HAYZUWEI 3,885,010

SHEET 2 G5: 2

Cl HIHHH no g PROCESS AND APPARATUS FOR THE CONTINUOUS MANUFACTURE OFPI-IENOLIC RESIN FOAM IN ENDLESS SHEETS This invention relates to aprocess for the continuous manufacture of phenolic resin foam in endlesssheets by mixing expandable liquid phenolic resins with a blowing agentand an acid-containing curing agent, optionally with an admixture ofadditives, and processing the mixture in a temperature-controllabledouble belt press.

It is conventional to spray expandable mixtures under pressure out of anozzle for the continuous production of foamed plastic sheets with theuse of a double belt press. The nozzle is moved, in this process, at ahigh velocity (e.g., about 200 m./min. and thereabove) to and fro overthe belt at right angles to the feeding diredtion of the belt. In orderto attain a more uniform distribution, it is also known to apply thefoam mixture, by means of a reciprocating device which moves slowly atright angles to the feeding direction, in a rough preliminarydistribution to the lower belt of the double belt press, and then topass the thus-applied mixture through the gap (of adjustable thickness)formed between 21 roll and a support, during which step the mixture isfinely distributed across the entire width of the belt to the desireduniform layer thickness. During the further pass through the double beltpress, the foaming and curing of the reaction mixture are thencarriedout.

It is the object of the present invention to improve the conventionalprocesses for the production of foamed sheets, particularly thoseintended for the manufacture of phenolic resin foam materials, in such amanner that a continuous process is made possible starting with themixing of the individual substances to obtain the expandable reactionmixture up to the finished, worked-up sheet offoam material, within aneconomical time period and by means of economical devices.

In accordance with the process of this invention, the expandablephenolic resin is cooled to a processing temperature of preferably about8 to about C. Thereafter, the blowing agent, which is under a highpressure, is admixed thereto, optionally under additional cooling; theresin-blowng agent premix is then mixed with additives and curing agentsand continuously applied in a reciprocating manner and uniformlydistributed onto a moving substrate entering the double belt press; thepremix on the substrate is covered with a top layer; then, in the heatof the heated double belt press, the mixture is continuously expanded inthe vertical direction until the desired sheet thickness has beenobtained and is sufficiently cured at an adjustable blowing pressure ofpreferably about 0.1 to about 0.3 atmosphere gauge until the sheet isdischarged from the double belt press. Thereafter, the phenolic resinfoam sheet is passed to further processing, such as foaming into panels.

By means of the process of this invention, wherein special emphasis isplaced on maintaining specific operating temperatures during the mixing,distribution, and expansion of the substances, it is made possible tomanufacture, in a continuous procedure, endless foam sheets of phenolicresin. By the temperature control and pressure regulation in the doublebelt press, the foaming period and the curing time are kept within suchlimits that economically feasible constructional lengths of the doublebelt press are made possible and, at the same time, a phenolic resinfoam material is obtained which is of a uniform and fine-poredstructure.

Additional features and advantages of the process and the apparatus ofthis invention for effecting the continuous manufacture of phenolicresin foam sheets are described in greater detail with reference tospecific embodiments and to the accompanying drawings in which:

FIG. 1 is a flow diagram illustrating the process for the continuousproduction of phenolic resin foam sheets;

FIG. 2 schematically shows an apparatus for producing the phenolic resinfoam sheets with a double belt press; and

FIG. 3 shows the heating mechanism of the double belt press of FIG. 2.

As shown in FIG. 1, the components for producing the phenolic resin foamare stored in storage tanks. In tank 1 is an expandable phenolic resin,e.g. the phenolic foaming compound produced by Dynamit Nobel AG. anddesignated T 612 S and a blowing agent e.g., n-pentanc, is in tank 2. Intank 3 an acid curing agent e.g., a mixture of 40% by weight ofp-toluenesulfonic acid, 20% by weight of concentrated sulfuric acid, and40% by weight of water,'is stored and there are furthermore provided thetank 4 for liquid to pasty modifiers, e.g., trichloroethyl phosphate ormineral oils, or mixtures of boric acid with such substances, and thetank 5 for pulverized additives, e.g., gypsum (plaster of Paris). Thesecomponents are fed via metering devices 6, 7, 8, 9, 10, such as, forexample, dosing pumps, associated with the individual tanks, to themixing device 12 or 13 as shown. The basic component, the phenolic resintaken from tank 1, is subjected, during the metering procedure (i.e.,when passing from tank 1 via the metering pump 6 into the premixingdevice 12) to an intense cooling in a screw-type indirect cooler 11. Thecoolant employed in the cooler has a cooling temperature of about +4C.to about 4C., whereby the processing temperature of the phenolic resinis attained. This processing temperature ranges between about 8C. andabout 15C.; whereas the inlet temperature of the resin from the storagetank is from about 20C. to 25C. In order to be able to obtain an optimumcooling of the phenolic resin, the number of revolutions of the screwconveyor disposed in the screw-type cooler 11 can be widely varied bymeans of a variable speed gear. Additionally, pressure equalization isobtained in the cooler 11 between the inlet and outlet thereof, via thisspeed control of the conveyor. The screw conveyor and the cylinder areboth cooled. The thus-cooled phenolic resin 1 then enters a premixingdevice 12, wherein, with the addition of blowing agent 2, e.g.,n-pentane, an intense, extremely fine distribution of the blowing agenttakes place throughout the premixing device 12, which is equipped with adouble-vane helix mixer. The blowing agent 2 is fed or introduced via ametering pump 7 and a spring-loaded valve arranged at premixing device12, under' a pressure of about 50 atmospheres guage. Due to this highpressure, the blowing agent is atomized and, at the same time, thephenolic resin 1 is prevented from flowing into the blowing agent feedconduit.

In order to mix the phenolic resin with the blowing agent, the premixingdevice 12 is preferably constructed in the form of two series-connectedpremixing chambers 12' (as shown in FIG. 2). The two premixing chambersemployed can be cooled with a coolant, preferably with a temperature of+4C. to -4C. However, the two premixing chambers 12 may be cooledindividually, so that, when the thus-introduced phenolic resin hasalready been sufficiently cooled, the cooling of the first premixingchamber 12 can be omitted. Thereby, any rise or increase in viscositywhich may occur due to the fact that the resin is cooled too much isavoided and an optimum mixing is attained. The second premixing chamber12' is cooled in any event, in order to avoid an increase in thetemperature of the mixture, caused by frictional heat, to above thetemperature value still feasible for processing.

The mixing of all components into a curable and foamable compositiontakes place subsequently in the mixing device 13. During start-up of theplant, the components are to be fed to the mixing device 13 in thefollowing succession:

l. metered feeding of the additives from tanks 4 and 2. metered feedingof the phenolic resin pentane mixture obtained fromtanks 1 and 2;

3. metered feeding of the curing agent from tank 3.

When charging the final mixing device 13 with the required components,it is to be considered that the mixing procedure is to be effected overa longer production period of, for example, 120 hours, for thecontinuous manufacture of endless sheets, without any disturbances. Forthis purpose, a specially developed mixing mechanism is utilized whichmakes it possible to conduct continuous mixing without any impairment ofthe mixing procedure due to premature curing of the mixture. In themixing device 13, the mixing chamber is subdivided into a chamber forthe metered introduction of the phenolic resin-blowing agent mixture andinto a mixing chamber for the metered feeding of the curing agent andthe additives. A single, continuous mixing shaft effects the intermixingin this device. By the formation of a pressure gradient in the junctiongap between the two chambers, the return of the curable mixture into thechamber containing the mixer shaft bearings is prevented, so thatclogging of the mixer shaft is forestalled. A device of this type isdisclosed in applicants copending application Ser. No. 231,1 l2, filedon Mar. 2, 1972.

The discharge of the reaction mixture from the mixing device 13 takesplace via the flexible foaming hose 23, the mouth of which isreciprocated by means of a reciprocating mechanism, e.g., areciprocatory gear, over the continuously fed substrate or base sheet 42shown in FIG. 2. This results in a preliminary distribution of the resinmixture. The final distribution of the mixture takes place by way of thedistributing roll 22 which makes it possible to distribute the mixtureaccurately on the sheet 42 and which functions simultaneously as a guideroll for the continuously entering top sheet 43.

The quality of the product, i.e., the structure and the homogeneousdistribution of the components, depends particularly upon the extremelyfine distribution of the blowing agent in the phenolic resin.

This distribution is achieved by the provision of, for example, the twopremixing chambers, each having a rotational mixing speed that isvariable, so that an optimal speed corresponding to the weight rate offlow, or throughput, of the phenolic resin can be set or adjusted 4 (forinstance within the range of 800 to 1,600 revolutions per minute).

In addition thereto, the cooling of the premixing chambers 12 has theeffect of influencing the temperature of the mixture and the mixingintensity since the mixing capacity, or mixability, between resin andblowing agent (for example n-pentane) depends to a large extent on theresin temperature and since with an increasing temperature, andconsequently decreasing viscosity, the mixture formation is facilitated.The mixture produced in this manner from resin and blowing agent isprocessed, or treated in the final mixing device 13 to a reactive and,respectively, hardenable mixture with the addition of the hardener orcuring agent and other additives.

In connection with this mixture formation, care should be taken toinsure that the temperature of the mixture discharging from the finalmixing device 13 will not exceed 30C. I

The optimal mixing effect with, at the same time, a short starting time(the time between the beginning of the mixture up to the recognizablevolume increase) is obtained in the range of between 28C. and 30C. Abovethat temperature, a so-called frothing will set in. This phenomenon mustbe prevented with absolute certainty since in that case, in the processdescribed, a uniform mixture distribution over the distributing roll 22is no longer possible inasmuch as material accumulations are formed inthe area of the reversing points of the mixture hose 23 being moved withaid of a lifting or reciprocating gear.

In order to meet the requirement for limiting the temperature of thefinished mixture to 30C., the temperature of the phenolic resin beingemployed must amount to approximately 5C. to approximately 12 to 15C.

for a weight rate of flow of, for example, from about 1 kg/min to about5 kg/min.

The higher phenolic resin temperature is suitable for the greater weightrate of flow or throughput and is due to the fact that, with thevariable mixing chambers, the residence time is reduced and theattainment of an optimal mixture is guaranteed by the reduction of theresin viscosity.

As shown in FIG. 2, after the mixture has been disposed, in theunexpanded (or pre-expanded) form, between the protective layersprovided by sheets 42, 43 and has entered the belt mold formed by theupper belt 26 and the lower belt 27 of the double belt press, the actualfoaming and curing procedure begins. The foaming and curing procedure isinitiated by the exothermic heat of reaction and by the heat of. theheated belt press. The mixture is expanded under the formation of a moreor less slightly increasing foaming angle. The belt speed, in thisconnection, is adjusted so that a continuous and vertical foaming of themixture is ensured. The foaming process takes place until the thicknessset by the belt spacing is achieved, and thereafter the mixturecommences the curing process without any additional foaming movements,under the buildup of a foaming pressure. The foaming pressure ismeasured and adjusted in such a manner that it does not exceed about 0.3atmosphere guage; preferably, this pressure ranges between about 0.1atmosphere gauge and about 0.3 atmosphere gauge. The curing processtakes about 6 to about 9 minutes, depending on the resin charge beingprocessed.

The quality of the thus-produced sheet of foam material can be affectedduring this curing process by way of the belt temperature, thereactivity of the phenolic resin and/or the exothermic heat of reactionthereof during the foaming and curing reaction, the proportion ofpropellant, and the proportion of curing agent, and the additives. Theendless phenolic resin foam sheet 31, sufficiently cured after leavingthe belt press, is provided with the protective cover layers formed bysheets 42 and 43. These cover layers can be fashioned as adherent ornon-adherent cover layers, so that they can be removed, if desired.

For the production of sheet stock without cover layers, a non-adherentrelease paper or liner material is introduced in the same manner as anormally adherent cover layer, and pulled off continuously by means ofthe device 29, 30 after the foamed sheets have exited from the beltpress. The phenolic resin foam sheets produced without adherent coverlayers are distinguished, in contrast to the sheets cut from a foamedblock, by a particularly'smooth, dust-free surface which therefore doesnot impede any adhesive effect.

The sheets produced according to this invention with or without adherentcover layers exhibit a density gradient which improves the antislipbehavior. The density of the phenolic resin foam increases from thecenter of the sheet to the external zones by about Directly downstreamof the double belt press, there follows the devices for the finishing ofthe material, denoted by 33, 34 and for the grooving of the sheets,denoted by 32, 36, and 37. It proved to be advantageous, for theavoidance of' warping phenomena, especially when the phenolic resin foampanels are used in the construction field, to provide the phenolic resinfoam panels with longitudinal and transverse grooves. These grooves aresuitably disposed in a parallel relationship and bilaterally offset withrespect to one another. The depth of the grooves is dependent on thethickness of the panels, and the base of the grooves is advantageouslyof a semicircular shape. The grooving at right angles to themanufacturing direction takes place in a transverse grooving device 37disposed separately from the cutting device 34 and provided with aconveying means 36. This arrangement can be seen clearly from FIG. 2.

Also the construction of the double belt press can be seen in greaterdetail from FIG. 2. The belt arrangement consists of the bottom belt 27and the heightadjustable top belt 26. The belts 26 and 27 are composedof individual belt plates and revolve by way of roller chains. The beltmold formed by the top and bottom belts is laterally closed off ordefined by limiting rubber elements rotating with the bottom belt 27. Inorder to ensure the lateral seal in the thus-formed in the thus-formedbelt when the foaming pressure occurs, the margin-limiting rubberelements 25 are guided by rods disposed. on the upper and lower beltplates. The adjustment of the top belt 26 to the desired height of thebelt mold is effected, for example, by means of hydraulic cylinders 28,and the fixation of the top belt 26 is accomplished by appropriatespacers.

The thickness adjusting range of the belt mould range between 20 mm. and100 mm. For the different sheet thicknesses to be produced in eachindividual case, a corresponding pair of margin-limiting rubber elements25 are required. The belt mold height of the top belt 26, correspondingto the thickness of the foamed sheet,

is constant up to a maximally permissible foaming pressure. When thismaximally allowable foaming pressure, which is measured, is exceeded, alarger thickness of the foamed sheet is produced which corresponds tothe maximally permissible foaming pressure, by an automatic lifting ofthe top belt 26.

The heat necessary for the foaming and curing process is obtained,interalia, by an intense temperature control of thebelt arrangementwhich is as uniform as possible. The belt temperatures are from about50C. to about C., depending on the phenolic resin foam quality to beproduced, in dependence on the recipe of the mixture employed. The beltarrangement is heated, for example, with hot air. The conductance of thehot air can be seen from FIG. 3, wherein the hot-air fan 39 blows theair through the radiator 40, and the hot air is then guided around thebelts 26 and 27. Within the belt press, an additional heater 41 is alsoarranged.

The cover layers provided by sheets 43 and 43 are wound as webs on thetake-off devices 14 and 17 and are introduced into the belt press viaguide rolls. In order to ensure an accurate feed of the cover sheets 42and 43 into the belt press, an edge control 15, 18, actuated bypneumatic-hydraulic means, is provided for both cover sheets.

In order to avoid contamination with reaction mixture, the edges of thelower cover sheet 42 are bent upwardly by via the device 20. The edgeheight is to be chosen so that an overlapping of the foam sheetthickness by about 10 mm. is attained. The reaction mixture isintroduced into this box-shaped cover sheet 42. The upper cover sheet 43introduced via the distributor roll 22 constitutes the lid 'of the boxform which is open at the top. The upright edges of the lower coverlayer are then bent inwardly by means of the further device 24 andenvelop the edges of the upper cover layer. The mixture expanding in thebelt-press then pushes the upper cover sheet 43 up to the upper limit ofthe edges of the lower cover sheet. Due to the foaming pressure whichbuilds up, the upper cover sheet is pressed against the bent strips ofthe lower cover sheet. Thus, a seal is ensured thereby against anyexiting mixture.

In order to improve the-adhesive or release effect of the cover sheets42 and 43 on the phenolic resin foam, apparatus 16 and 19 are arrangeddirectly upstream of the point where the reaction mixture is applied,for the coating or impregnation of the cover sheets with specificsubstances, e.g. adhesives or release agents.

It will be appreciated that the nature of the phenolic resin, andblowing agent and the acid curing agent are further exemplified inpending application Ser. No. 31,418 filed on Apr. 23, 1970, nowabandoned, by two of the inventors in the subject application.Accordingly, this application is incorporated by reference in thesubject application.

.What is claimed is:

1. In a process for the continuous manufacture of phenolic resin foam inan endless sheet by mixing a liquid phenolic resin with a blowing agentand an acidcontaining curing agent and by processing of the mixture in atemperature-controllable double belt press, the improvement whichcomprises cooling the liquid phenolic resin to a temperature of fromabout 8 to about 15C., admixing a blowing agent under a high pressurewith said resin to form a resin premix, mixing said resin premix with acuring agent to form a curable reaction mixture, continuously applyingsaid mixture uniformly onto a moving substrate, covering the mixture onsaid substrate with a continuous protective layer, passing the coveredmixture in the double belt press, and foaming the mixture under pressureuntil said sheet is formed.

2. The process of claim 1, wherein the phenolic resin is mixed with theblowing agent in a first premixing chamber and thereafter is furtherintermixed in a second premixing chamber with simultaneous cooling ofthe mixture.

3. The process of claim 1, wherein the substrate and cover layercontacting phenolic resin foam are treated, immediately prior to cominginto contact with the curable reaction mixture, with an adhesive orrelease agent.

4. The process of claim 1, wherein the blowing pressure of the foamduring foaming is maintained to within a predetermined pressure range byvarying the sheet thickness of the foaming reaction mixture.

5. The process of claim 4, wherein the blowing pressure is from about0.1 to about 0.3 atmosphere gauge.

6. Process of claim 1, wherein the substrate and the top cover layersurround the expanded sheet on all sides of the foam.

7. The process of claim 6, wherein the top cover layer is disposedwithin a U-shaped channel formed by the substrate.

8. A process for the continuous production of phenolicresin foam inendless sheets comprising cooling a liquid phenolic resin to 8 to C,mixing the thus cooled liquid phenolic resin with a blowing agent toresin'with said premix to form an expandable and hardenable liquidphenolic reaction mixture, continuously applying said liquid phenolicreaction mixture onto a continuously moving lower cover layer from anozzle reciprocating transversely to the direction of movement of saidlower cover layer, covering the reaction mixture on said lower coverlayer with an upper cover layer, passing the covered mixture between thebelts of a double belt press, and heating the covered mixture whilebetween the belts of said double belt press so that said reactionmixture is foamed under pressure and at least partially cured whereby aphenolic resin foam sheet having a predetermined thickness is formed.

9. The process according to claim 8, wherein modifiers or fillers areadded to the liquid phenolic resin simultaneously with the addition ofthe curing agent.

10. The process according to claim 8, wherein said lower cover layer isbent upwardly in a U-shape so that said lower cover layer definesupwardly extending edges on each lateral side thereof, said processfurther comprising inwardly bending the ends of said upwardly extendingedges about the lateral edges of said upper cover layer.

11. The process according to claim 8, wherein the blowing pressure ofsaid reaction mixture as it foams is maintained to within apredetermined range by controlling the distance between the belts insaid double belt press and hence the thickness of said sheet.

12. The process according to claim 11, wherein the blowing pressure ofsaid reaction mixture during foaming is maintained between about 0.1 and0.3 atmosphere gauge by controlling the thickness of the sheet producedwith the belts of said double belt press.

. form a premix, mixing a curing agent for the phenolic 13. The processaccording to claim 8, wherein said covered mixture is heated in saiddouble belt press by means of hot air.

14. The process according to claim 13, wherein the temperature of saidhot air is maintained such that the temperatures of the belts in saiddouble belt press are between about 50 to C.

15. The process according to claim 8, wherein said blowing agent is fedto said liquid phenolic resin at a pressure sufficiently high so that itis atomized.

16. The process according to claim 15, wherein said blowing agent is fedto said liquid phenolic resin at a pressure of about 50 atmospheresgauge.

17. The process according to claim 8, wherein said blowing agent andsaid liquid phenolic resin are mixed in a chamber cooled to atemperature of about +4C to 18. The process according to claim 8,wherein said blowing agent is mixed with said liquid phenolic resin intwo pre-mixing chambers, at least one chamber being cooled to betweenabout +4C and 4C.

19. The process according to claim 8, wherein said blowing agent ishomogeneously mixed with said liquid phenolic resin in a chamber.

20. The process according to claim 8, wherein said reaction mixturefurther includes modifiers or fillers.

21. The process according to claim 8, wherein said reaction mixtureafter being deposited on said lower cover layer is uniformly distributedthereon by means of a guide roll.

' 22. The process according to claim 21, wherein said upper-cover layeris guided by said guide roll.

23. The process according to claim 8, wherein the temperatureof saidreaction mixture is no more than about 30C as it is applied to saidlower cover layer.

24. The process according to claim 23, wherein said reaction mixture ismaintained between-about 28 and 30C as it is applied to said lower coverlayer.

25. The process according to claim 8, wherein the weight flow rate ofthe reaction mixture is about 1 to 5 kg/min.

26. The process according to claim 8, further comprising forming groovesin the phenolic resin foam sheet passing out of the double belt press.

27. The process according to claim 8, wherein the phenolic resin foamsheet passing out of said double belt press has a thickness of at leastabout 20 min.

28. The process according to claim 27, wherein the' phenolic resin foamsheet has a thickness of about 20 to mm.

29. In a process for the continuous production of a phenolic resin foamin endless sheet form by continuously feeding a mixture of a liquidphenolic resin, a blowing agent and an acid-containing curing agentbetween the belts of a double belt press and heating the mixture whilein said press to cause the mixture to foam and cure between the belts insaid press, the improvement comprising cooling said liquid phenolicresin to a temperature of between about 8 to 15C prior to mixing withthe blowing agent and curing agent.

30. In a process for the continuous production of phenolic resin foam inendless sheet form by mixing a liquid phenolic resin with the blowingagent and subsequently with the acid-containing curing agent, feedingthe mixture so obtained in a transversely reciprocating manner betweenthe belts of a double belt press, and continuously foaming and curingthe mixture as it travthat said mixture uniformly distributed on saidlower cover layer, bending the ends of the upwardly extending edges ofthe lower U-shaped cover layer inwardly about the lateral edges of theupper cover layer, and maintaining the foaming pressure of the mixtureas it vertically foams to within a predetermined pressure range.

1. IN A PROCESS FOR THE CONTINUOUS MANUFACTURE OF PHENOLIC RESIN FOAM INAN ENDLESS SHEET BY MIXING A LIQUID PHENOLIC RESIN WITH A BLOWING AGENTAND AN ACID-CONTAINING CURING AGENT AND BY PROCESSING OF THE MIXTURE INA TEMPERATURE-CONTROLLABLE DOUBLE BELT PRESS, THE IMLPROVEMENT WHICHCOMLRISES COOLING THE LIQUID PHENOLIC RESIN TO A TEMPERATURE OF FROMABOUT 8* TO ABOUT 15*C., ADMIXING A BLOWING AGENT UNDER A HIGH PRESSUREWITH SAID RESIN TO FORM A RESIN PREMIX, MIXING SAID RESIN PREMIX WITH ACURING AGENT TO FORM A CURABLE REACTION MIXTURE, CONTINUOUSLY APPLYINGSAID MIXTURE UNIFORMLY ONTO A MOVING SUBSTRATE, COVERING THE MIXTURE ONSAID SUBSTRATE WITH A CONTINUOUS PROTECTIVE LAYER, PASSING THE COVEREDMIXTURE IN THE DOUBLE BELT PRESS, AND FOAMING THE MIXTURE UNDER PRESSUREUNTIL SAID SHEET IS FORMED.
 2. The process of claim 1, wherein thephenolic resin is mixed with the blowing agent in a first premixingchamber and thereafter is further intermixed in a second premixingchamber with simultaneous cooling of the mixture.
 3. The process ofclaim 1, wherein the substrate and cover layer contacting phenolic resinfoam are treated, immediately prior to coming into contact with thecurable reaction mixture, with an adhesive or release agent.
 4. Theprocess of claim 1, wherein the blowing pressure of the foam duringfoaming is maintained to within a predetermined pressure range byvarying the sheet thickness of the foaming reaction mixture.
 5. Theprocess of claim 4, wherein the blowing pressure is from about 0.1 toabout 0.3 atmosphere gauge.
 6. Process of claim 1, wherein the substrateand the top Cover layer surround the expanded sheet on all sides of thefoam.
 7. The process of claim 6, wherein the top cover layer is disposedwithin a U-shaped channel formed by the substrate.
 8. A process for thecontinuous production of phenolic resin foam in endless sheetscomprising cooling a liquid phenolic resin to 8* to 15*C, mixing thethus cooled liquid phenolic resin with a blowing agent to form a premix,mixing a curing agent for the phenolic resin with said premix to form anexpandable and hardenable liquid phenolic reaction mixture, continuouslyapplying said liquid phenolic reaction mixture onto a continuouslymoving lower cover layer from a nozzle reciprocating transversely to thedirection of movement of said lower cover layer, covering the reactionmixture on said lower cover layer with an upper cover layer, passing thecovered mixture between the belts of a double belt press, and heatingthe covered mixture while between the belts of said double belt press sothat said reaction mixture is foamed under pressure and at leastpartially cured whereby a phenolic resin foam sheet having apredetermined thickness is formed.
 9. The process according to claim 8,wherein modifiers or fillers are added to the liquid phenolic resinsimultaneously with the addition of the curing agent.
 10. The processaccording to claim 8, wherein said lower cover layer is bent upwardly ina U-shape so that said lower cover layer defines upwardly extendingedges on each lateral side thereof, said process further comprisinginwardly bending the ends of said upwardly extending edges about thelateral edges of said upper cover layer.
 11. The process according toclaim 8, wherein the blowing pressure of said reaction mixture as itfoams is maintained to within a predetermined range by controlling thedistance between the belts in said double belt press and hence thethickness of said sheet.
 12. The process according to claim 11, whereinthe blowing pressure of said reaction mixture during foaming ismaintained between about 0.1 and 0.3 atmosphere gauge by controlling thethickness of the sheet produced with the belts of said double beltpress.
 13. The process according to claim 8, wherein said coveredmixture is heated in said double belt press by means of hot air.
 14. Theprocess according to claim 13, wherein the temperature of said hot airis maintained such that the temperatures of the belts in said doublebelt press are between about 50* to 80*C.
 15. The process according toclaim 8, wherein said blowing agent is fed to said liquid phenolic resinat a pressure sufficiently high so that it is atomized.
 16. The processaccording to claim 15, wherein said blowing agent is fed to said liquidphenolic resin at a pressure of about 50 atmospheres gauge.
 17. Theprocess according to claim 8, wherein said blowing agent and said liquidphenolic resin are mixed in a chamber cooled to a temperature of about+4*C to -4*C.
 18. The process according to claim 8, wherein said blowingagent is mixed with said liquid phenolic resin in two pre-mixingchambers, at least one chamber being cooled to between about +4*C and-4*C.
 19. The process according to claim 8, wherein said blowing agentis homogeneously mixed with said liquid phenolic resin in a chamber. 20.The process according to claim 8, wherein said reaction mixture furtherincludes modifiers or fillers.
 21. The process according to claim 8,wherein said reaction mixture after being deposited on said lower coverlayer is uniformly distributed thereon by means of a guide roll.
 22. Theprocess according to claim 21, wherein said upper cover layer is guidedby said guide roll.
 23. The process according to claim 8, wherein thetemperature of said reaction mixture is no more than about 30*C as it isapplied to said lower cover layer.
 24. The process according to claim23, wherein said reaction mixture is maintained between about 28* and30*C as it is applied to said lower cover layer.
 25. The processaccording to claim 8, wherein the weight flow rate of the reactionmixture is about 1 to 5 kg/min.
 26. The process according to claim 8,further comprising forming grooves in the phenolic resin foam sheetpassing out of the double belt press.
 27. The process according to claim8, wherein the phenolic resin foam sheet passing out of said double beltpress has a thickness of at least about 20 min.
 28. The processaccording to claim 27, wherein the phenolic resin foam sheet has athickness of about 20 to 100 mm.
 29. In a process for the continuousproduction of a phenolic resin foam in endless sheet form bycontinuously feeding a mixture of a liquid phenolic resin, a blowingagent and an acid-containing curing agent between the belts of a doublebelt press and heating the mixture while in said press to cause themixture to foam and cure between the belts in said press, theimprovement comprising cooling said liquid phenolic resin to atemperature of between about 8* to 15*C prior to mixing with the blowingagent and curing agent.
 30. In a process for the continuous productionof phenolic resin foam in endless sheet form by mixing a liquid phenolicresin with the blowing agent and subsequently with the acid-containingcuring agent, feeding the mixture so obtained in a transverselyreciprocating manner between the belts of a double belt press, andcontinuously foaming and curing the mixture as it travels through saidpress, the improvement comprising cooling said liquid phenolic resin toa temperature of about 8* to 15*C prior to admixture with said blowingagent, continuously applying said mixture in a transverselyreciprocating manner onto a lower cover layer having a U-shaped crosssection and defining upwardly extending lateral edges, applying an uppercover layer to the mixture on said lower cover layer in such a way thatsaid mixture uniformly distributed on said lower cover layer, bendingthe ends of the upwardly extending edges of the lower U-shaped coverlayer inwardly about the lateral edges of the upper cover layer, andmaintaining the foaming pressure of the mixture as it vertically foamsto within a predetermined pressure range.